devlink: fix xa_alloc_cyclic error handling

Pierre Riteau <[email protected]> found suspicious handling an error
from xa_alloc_cyclic() in scheduler code [1]. The same is done in
devlink_rel_alloc().

In case of returning 1 from xa_alloc_cyclic() (wrapping) ERR_PTR(1) will
be returned, which will cause IS_ERR() to be false. Which can lead to
dereference not allocated pointer (rel).

Fix it by checking if err is lower than zero.

This wasn't found in real usecase, only noticed. Credit to Pierre.

Signed-off-by: Michal Swiatkowski <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: Michal Swiatkowski

net/devlink/core.c

@@ -117,7 +117,7 @@ static struct devlink_rel *devlink_rel_alloc(void)
 
 	err = xa_alloc_cyclic(&devlink_rels, &rel->index, rel,
 			      xa_limit_32b, &next, GFP_KERNEL);
-	if (err) {
+	if (err < 0) {
 		kfree(rel);
 		return ERR_PTR(err);
 	}